The present invention is directed to communication systems and, more particularly, to a technique for detecting, identifying, extracting and eliminating narrowband interference in a wideband communication system.
As shown in FIG. 1, an exemplary telecommunication system 10 may include mobile units 12, 13, a number of base stations, two of which are shown in FIG. 1 at reference numerals 14 and 16, and a switching station 18 to which each of the base stations 14, 16 may be interfaced. The base stations 14, 16 and the switching station 18 may be collectively referred to as network infrastructure.
During operation, the mobile units 12, 13 exchange voice data or other information with one of the base stations 14, 16, each of which are connected to a conventional land line telephone network. For example, information, such as voice information, transferred from the mobile unit 12 to one of the base stations 14, 16 is coupled from the base station to the telephone network to thereby connect the mobile unit 12 with a land line telephone so that the land line telephone may receive the voice information. Conversely, information, such as voice information may be transferred from a land line telephone to one of the base stations 14, 16, which, in turn, transfers the information to the mobile unit 12.
The mobile units 12, 13 and the base stations 14, 16 may exchange information in either analog or digital format. For the purposes of this description, it is assumed that the mobile unit 12 is a narrowband analog unit and that the mobile unit 13 is a wideband digital unit. Additionally, it is assumed that the base station 14 is a narrowband analog base station that communicates with the mobile unit 12 and that the base station 16 is a wideband digital base station that communicates with the mobile unit 13.
Analog format communication takes place using narrowband 30 kilohertz (KHz) channels. The advanced mobile phone systems (AMPS) is one example of an analog communication system in which the mobile unit 12 communicates with the base station 14 using narrowband channels. Alternatively, the mobile unit 13 communicates with the base stations 16 using a form of digital communications such as, for example, code-division multiple access (CDMA) or time-division multiple access (TDMA). Digital communication takes place using spread spectrum techniques that broadcast signals having wide bandwidths, such as, for example, 1.25 megahertz (MHz) bandwidths.
The switching station 18 is generally responsible for coordinating the activities of the base stations 14, 16 to ensure that the mobile units 12, 13 are constantly in communication with the base station 14, 16 or with some other base stations that are geographically dispersed. For example, the switching station 18 may coordinate communication handoffs of the mobile unit 12 between the base stations 14 and another analog base station as the mobile unit 12 roams between geographical areas that are covered by the two base stations.
One particular problem that may arise in the telecommunication system 10 is when the mobile unit 12 or the base station 14, each of which communicate using narrowband channels, interfere with the ability of the base station 16 to receive and process wideband digital signals from the digital mobile unit 13. In such a situation, the narrowband signal transmitted from the mobile unit 12 or the base station 14 may interfere with the ability of the base station 16 to properly receive wideband communication signals.
According to one aspect, the present invention may be embodied in a method of detecting and eliminating narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein. Such a method may include scanning at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels and determining a threshold based on the signal strengths in at least some of the narrowband channels. Additionally, the method may include identifying narrowband channels having signal strengths exceeding the threshold and assigning filters to at least some of the narrowband channels having signal strengths exceeding the threshold. Furthermore, the method may include determining if the assigned filters are operating properly and bypassing any of the assigned filters that are not operating properly.
According to a second aspect, the present invention may be embodied in a system adapted to detect and eliminate narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein. Such a system may include a scanner adapted to scan at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels, a notch module adapted to receive the wideband communication signal and to selectively remove narrowband interference from the wideband communication signal to produce a filtered wideband communication signal and a bypass switch adapted to bypass the notch module when the bypass switch is enabled. Furthermore, the system may include a controller coupled to the scanner and to the notch module, wherein the controller is adapted to determine a threshold based on the signal strengths in at least some of the narrowband channels. Furthermore, the controller may be adapted to identify narrowband channels having signal strengths exceeding the threshold, to control the notch module to filter the wideband communication signal at a frequency corresponding to a narrowband channel having a signal strength exceeding the threshold, to determine if the notch module is operating properly and to enable the bypass switch when the notch module is not operating properly.
According to a third aspect, the present invention may be embodied in a method of detecting and eliminating narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein. Such a method may include scanning at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels, determining a threshold based on the signal strengths in at least some of the narrowband channels and identifying fading narrowband channels having signal strengths that do not exceed the threshold and that were previously identified as exceeding the threshold, based on how long the identified narrowband channels have not exceeded the threshold. Additionally, the method may include filtering the wideband communication signal at a frequency corresponding to a fading narrowband channel.
According to a second aspect, the present invention may be embodied in a system adapted to detect and eliminate narrowband interference in a wideband communication signal having a frequency bandwidth with narrowband channels disposed therein. Such a system may include a scanner adapted to scan at least some of the narrowband channels to determine signal strengths in at least some of the narrowband channels in an order representative of a probability that the narrowband channels will have interference and a notch module adapted to receive the wideband communication signal and to selectively remove narrowband interference from the wideband communication signal to produce a filtered wideband communication signal. The system may also include a controller coupled to the scanner and to the notch module, wherein the controller is adapted to determining a threshold based on the signal strengths in at least some of the narrowband channels. The controller may be further adapted to identify fading narrowband channels having signal strengths that do not exceed the threshold and that were previously identified as exceeding the threshold, based on how long the identified narrowband channels have not exceeded the threshold and to control the notch module to filter the wideband communication signal at a frequency corresponding to a fading narrowband channel.
These and other features of the present invention will be apparent to those of ordinary skill in the art in view of the description of the preferred embodiments, which is made with reference to the drawings, a brief description of which is provided below.